http://www.kernel.org The Linux Kernel Archives. Where to find the latest kernel and more information.
http://www.kernel.org/mirrors Download the kernel from a server near you.
http://www.kernel-traffic.org The Kernel Traffic newsletter, a weekly summary of what's happening on the Kernel mailing list.
http://www.gnu.org GNU's not Unix. The home of many kernel-related projects. Get software and documentation here, and a healthy dose of free-software philosophy.
http://www.gnu.org/software/make/manual/make.html The make manual. This utility is much more than a source-code build environment.
http://kniggit.net/wwol26.html The Wonderful World of Linux 2.6, a guide to the latest version of the kernel by Joseph Pranevich.
http://www.kernelnewbies.org For people who want to try their hand at kernel hacking. The Kernel Newbies host an IRC chat channel, #kernelnewbies, and a wiki from this site.
http://tldp.org/LDP/lki Linux Kernel 2.4 Internals Guide. Get into more depth about how the kernel works.
http://tldp.org/HOWTO/HOWTO-INDEX/os.html#OSKERNEL These HOWTOs explore the kernel in several ways.
http://minix1.hampshire.edu Al Woodhull's Minix site. Learn more about Linux's "parent" OS.
http://www.cs.vu.nl/~ast/minix.html The official Minix site.
http://jungla.dit.upm.es/~jmseyas/linux/kernel/hackers-docs.html Its origins are similar to those of a FAQ document, but this annotated "Index of Documentation for People Interested in Writing and/or Understanding the Linux Kernel" is more of a reference guide, with pointers to an abundance of useful kernel information.
http://kerneltrap.org "Your Ultimate Source for Kernel News."
http://www.gnu.org/software/grub/manual The GRUB manual.
http://www.tldp.org/HOWTO/LILO.html The LILO mini-HOWTO.